Silicon carbide seal for an earth boring bit

ABSTRACT

A seal for containing lubricant in the bearings of an earthboring bit wherein the bit is used in a highly abrasive environment. At least one seal element encircles the shaft of the bit and retains lubricant in the bearings of the bit. The surface of the seal is silicon carbide and the seal will withstand a highly abrasive and corrosive environment.

United States Patent Inventor Carl L. Lichte Dallas County, Tex. Appl. No. 42,178 Filed June 1, 1970 Patented Sept. 14, 1971 Assignee Dresser Industries,1nc. Dallas, Tex.

SILICON CARBIDE SEAL FOR AN EARTH BORING BIT 13 Claims, 5 Drawing Figs.

US. Cl 175/372, 277/DIG. 6, 308/82 Int.Cl E21b 9/08, F16c 19/00 Field of Search 175/371,

References Cited UNITED STATES PATENTS Neilson Goodwin Hickernell Primary Examiner-.1 ames A. Leppink Attorneys-Robert W. Mayer, Thomas P. Hubbard, .lr., Daniel Rubin, Raymond T. Majesko, Roy L. Van Winkle, William E. Johnson, Jr. and Eddie E. Scott ABSTRACT: A seal for containing lubricant in the bearings of an earth-boring bit wherein the bit is used in a highly abrasive environment. At least one seal element encircles the shaft of the bit and retains lubricant in the bearings of the bit. The surface of the seal is silicon carbide and the seal will withstand a highly abrasive and corrosive environment.

PATENTEU SEP! 41% SHEET 1 [IF 2 INVENTOR CARL L. LICHTE ATTORNEY Pmmiusammn 3.604.523

SHEET 2 UF 2 INVENTOR CARL L. LICHTE FIG. 4 M1 1w ATTORNEY SILICON CARBIDE SEAL FOR AN EARTH BORING BIT BACKGROUND OF THE INVENTION This invention relates to the art of earth boring and, more particularly, to a seal between relatively rotatable members. This seal is positioned to retain lubricant between a shaft and a member which rotates about the shaft and to prevent the lubricant from being contaminated by drilling mud, cuttings or other foreign material.

Bits used for drilling by the rotary method generally include a main body with a multiplicity of shaft elements extending therefrom. Individual cutter elements are joumaled on said shafts. As the bit is rotated and moved through the formations, the cutter elements contact and disintegrate portions of the formation in order to form the desired borehole. A large portion of the cuttings produced by the drilling operation are in the form of finely divided particles which create a highly abrasive environment. In many drilling operations, a fluid such as drilling mud is circulated through the borehole in order to flush the cuttings. During the drilling operation, formations may be encountered which include various fluids. The fluids encountered by the bit may be corrosive and capable of damaging the bit. It can be appreciated that the seal must be adapted to prevent contamination of the lubricant and to withstand the corrosive and abrasive forces of the drilling environment.

In addition to being able to withstand the drilling environment, the seal must meet certain other requirements. The seal should occupy the minimum of space both radially and in an axial direction to avoid a reduction in thickness of the shell of the cutter element or in the diameter of the shaft. Any reduction in these elements would weaken the bit and reduce the space available for the bearing elements. It is highly desirable that as much room as possible be provided for the cutter shell and to maintain the size and strength of the shaft. Since the seal competes with the other working parts for the small amount of space available in a rotary drilling bit, it is desirable to limit the seal space and provide as much bearing space as possible.

The seal element should have and be able to maintain a good surface finish to reduce friction between the relatively rotatable members and insure a tight seal. In order to prevent overheating and loss of power, it is necessary to minimize friction in the rotary bit. The seal should be constructed from material having a low coefficient of friction. The seal also should have a long lifetime and not deform or deteriorate. As previously explained, the seal must be able to withstand the drilling environment because the bit must operate under highly abrasive conditions and may encounter corrosive fluids. The rotary bit may generate a large amount of heat, consequently the seal must be able to withstand high-temperature conditions.

DESCRIPTION OF THE PRIOR ART In U.S. Pat. No. 3,389,760 to W. E. Morris, patented June 25, 1968, a rolling cutter for an earth boring bit is shown. A series of seals are utilized to maintain lubricants in the bearings. In U.S. Pat. No. 3,449,024 to C. L. Lichte, patented June 10, 1969, a seal arrangement is shown for use in a highly abrasive environment. These two patents exemplify the general rolling cutter arrangement of an earth boring bit and the problems associated with maintaining lubricants in the bearings of the bit.

Another form of earth boring bit includes rolling cone cutters mounted on shafts extending from the main bit body. In U.S. Pat. No. 3,397,928 to E. M. Galle, patented Aug. 20, 1968, a seal means is shown for retaining lubricant in the bearings of a cone-type bit.

SUMMARY OF THE INVENTION The present invention provides a seal for retaining lubricant between a shaft and a relatively rotatable member. The seal has improved performance characteristics and a long life. The seal will withstand severe environmental conditions and resists wear.

Y The seal means encircles the shaft and provides a seal effective to retain lubricant in the bearings. The seal material is compatible with the environmental conditions, has a low coefficient of friction, resists wear and is suitable for the machine operations encountered in manufacturing.

It is therefore an object of the present invention to provide an effective seal for retaining lubricant between a shaft and a relatively rotatable member.

It is a further object of the present invention to provide a seal that is easy to manufacture and that will have high quality and reliable characteristics when it emerges from the manufacturing operation.

It is a still further object of the present invention to provide a seal that is compatible with highly abrasive, highly corrosive and high-temperature drilling conditions.

It is a still further object of the present invention to provide a seal that resists wear.

It is a still further object of the present invention to provide a seal that has a long lifetime.

The above and other objects and advantages will become apparent from a consideration of the following detailed description when taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. I shows a rolling cutter of an earth-boring bit. FIG. 2 is one embodiment of the seal of the present invention.

FIG. 3 is another embodiment of the seal of the present in- DETAILED DESCRIPTION OF THE INVENTION Referring now to FIG. I, a rolling cutter I0 is shown mounted in a saddle 11. A plurality of saddles and cutters are generally provided on a main bit body so that upon rotation of the bit, the cutters will contact and disintegrate portions of the formation. The cutter 10 rotates about a shell I2 with bearing means positioned between the cutter l0 and shell 12. The shell 12 provides the actual bearing surface for the bearing means and a surface for receiving the seals of this invention. A pin 13 extends through a central hole in shell 12 and is held by saddle 11. The shell 12 and pin 13 form a stable shaft about which the cutter 10 rotates.

The cutter 10 has means on its outer surfaces for disintegrating the formation. This means may take any one of numerous well known forms depending upon the type of formation in which it is to operate. As the bit is rotated and the cutters contact the formations, tremendous loads are imposed upon the bit. It is therefore essential that sufficient bearing means be provided and that the bearings be adequately lubricated. The bearing means may take the form of roller bearings 14 and 15 and ball bearings 16. In order to prevent failure of the bearings, a lubricant must be retained in the surrounding area.

In order to retain lubricant in the bearings, a pair of seal elements l7 and I8 are provided. A pair of mounting rings 19 and 20 are positioned between seal elements 17 and 18, respectively, and cutter I0. The mounting rings 19 and 20 are of a resilient material. The seal elements 17 and 18 are provided with a tapered surface to receive mounting rings 19 and 20 and mounting rings 19 and 20 are of such a dimension that when placed around the tapered surfaces of seals 17 and 18 they will be under tension circumferentially thereby providing a tight fit between seal elements 17 and 18 and the cutter 10. The seal elements 17 and 18 will therefore rotate with cutter 10 relative to shell 12.

Referring now to FIG. 2, seal elements 17 and 18 are shown in perspective with approximately one-half broken away and shown in cross section. The exterior portion of seal elements 17 and 18 is provided with tapered sections 21 and 22 for receiving the mounting rings as previously explained. The seal elements 17 and 18 have interior surfaces 23 and 24 that are rotatable with respect to shell 12. The interior surfaces 23 and 24 must maintain a smooth surface to provide an effective seal and reduce friction.

The seal elements 17 and 18 are preferably fabricated of graphite and coated with a dense, fluid impervious, beta crystalline, silicon carbide. The silicon carbide by reason of its chemical properties and impervious nature, protects seal elements l7 and 18from the abrasive, high temperature and corrosive environmental conditions. A method of applying a silicon carbide coating to a graphite base is disclosed in U.S. Pat. No. 3,250,322 to .l. W. McCrary, Jr. et al., patented May 10, i966. The graphite base should have a thermal coefficient of expansion approximately matching the thermal coefficient of expansion of the silicon carbide coating so that the seal elements may be used over a wide range of temperatures without rupturing the silicon carbide coating. The graphite may have a coefficient of thermal expansion in the range of from about 4.0Xl'a6 to about 5.4xl0 inch/inch/ C. The silicon carbide is extremely hard and therefore is resistant to the abrasive drilling conditions. In addition, machining operations of the seal elements are simplified and it is possible to obtain a smooth surface finish.

Referring now to FIG. 3, another embodiment of the seal of this invention is shown positioned between a rolling cutter 25 and shell 26 about which it rotates. The shell 26 forms a stable shaft for the cutter 25 to rotate about. The rolling cutter 25 is mounted in a saddle 27 and the saddle 27 forms a portion of a bit for drilling boreholes by the rotary method. The cutter 25 has means on its outer surfaces for disintegrating portions of the formation. This means may take the form of any of the well-known means presently used in the art. As the bit is rotated the cutters will contact and disintegrate portions of the formation to form the desired borehole.

The shell 26 provides the actual bearing surface for the bearing means and a surface for receiving the seals of this invention. The bearing means may take the form of roller bearings 27 and 28 and ball bearings 29. In order to prevent failure of the bearings, a lubricant must be retained in the area surrounding the bearings. Seal elements 30 and 31 are secured to shell 26 by providing mounting rings 32 and 33 between seal elements 30 and 31 and shell 26. A second pair of seal elements 34 and 35 are secured to cutter 25 by mounting rings 36 and 37. The mounting rings 32, 33, 36, and 37 are of a resilient material and serve to hold the seal elements in position. As the cutter 25 rotates seal elements 34 and 35 will rotate with the cutter element whereas seal elements 30 and 31 remain affixed to shell 26. A lubricant reservoir is thereby provided between the seal elements.

It can be appreciated that the surfaces of seal elements 30, 31, 34, and 35 must have a smooth surface to provide an effective seal and reduce friction. The seal elements are preferably fabricated of graphite and coated with a dense, fluid impervious, beta crystalline, silicon carbide. The silicon carbide by reason of its chemical properties and impervious nature, protects the seal elements from the abrasive, high temperature and corrosive environmental conditions. The graphite base should have a thermal coefficient of expansion approximately matching the thermal coefficient of expansion of the silicon carbide coating so that the seal elements may be used over a wide range of temperatures without rupturing the silicon carbide coating. The graphite may have a thermal coefficient of expansion in the range of from about 4.0Xl0 to about and therefo re is resistant to the ab rasi ve drilling conditions. In 75 addition, machining operations of the seal elements are simplifled and it is possible to obtain a smooth surface finish. It is to be understood that one pair of seal elements, either seal elements 30 and 31 or seal elements 34 and 35, could be of metal without departing from the scope of this invention. With one pair of the seal elements being of metal and the other pair having a silicon carbide surface, the seal would consist of a silicon carbide to metal seal arrangement rather than the silicon carbide to silicon carbide seal previously explained.

Referring now to FIG. 4, a partially cut away sectional view ofa rotatable cone-type earth-boring bit is indicated generally at 38. The bit 38 includes a body 39 with a threaded portion 40 for connecting the bit with the lower end of a rotary drill string (not shown). Bits of this character generally include three rolling cutters although a greater or lesser number of cutters may be employed. Two of the three cutters are shown in this view of the bit. Cutters 41 are rotatably attached to individual arms 42 depending from the main bit body 39. Each of the arms 42 is provided with a spindle 43 that projects therefrom into a recess 44 formed in each of the cutters 41. The cutters 41 are journaled on the spindle 43 by suitable bearing means such as roller bearings 44, ball bearings 45 or other bearings such as the button 46.

The individual rolling cone cutters have means for disintegrating the formations, positioned on their outer surfaces. The means for disintegrating the formations may take the form of individual cutting teeth, silicon carbide inserts or other well-known means of disintegrating the formations. The bit 38 is connected to a rotary drill string (not shown) by the threaded connection 40. As the bit is rotated, the cone cutters 41 contact the formation and disintegrate portions of the formation to form the desired borehole. The drill cuttings resulting from this operation are largely in the form of finely divided particles which creates a highly abrasive environment in the vicinity of the bit 38. in order to flush the drill cuttings from the borehole and to cool the bit, drilling mud is circulated down the rotary drill string and enters a recess 47 in the center of the bit. The drilling mud exits from an opening 48 in the bit and is directed to the rolling cone cutters. The drilling fluid then circulates upward in the annulus between the drill string and the borehole wall carrying with it the drill cuttings. During the drilling operation, the bit may encounter fluids in the formations and thereby be exposed to corrosive fluids of varying chemical composition. In order to prevent failure of the bearing means, a suitable lubricant should be retained in the area between the spindle 43 and the recess 44 in the rolling cone cutters 41. The seal of the present invention is provided to retain lubricant in the bearings and prevent contamination of the lubricant by fluids and particles in the borehole. A seal element 49 encircles the spindle 43. A resilient mounting ring 50 is positioned between seal element 49 and the cutters 41. The resilient mounting ring 50 is large enough to be placed in compression and will consequently insure that the seal element 49 will rotate with the cutters 41. The seal element 49 must be adapted to withstand the corrosive and abrasive environmental conditions encountered in the borehole.

The seal element 49 is shown in greater detail in FIG. 5 with approximately one-half broken away and shown in cross section. The seal element 49 is provided with a tapered section 51 for receiving the resilient mounting ring 50. The interior surface 52 of seal element 49 must maintain a smooth surface to insure an effectiveseal with spindle 43 and reduce friction. The seal element 49 is fabricated of graphite and coated with fluid impervious silicon carbide. The graphite should have a thermal coefficient of expansion approximately matching the thermal coefficient of expansion of the silicon carbide coating so that the seal may be used over a wide range of temperatures without rupturing the silicon carbide coating. The graphite may have a coefficient of thermal expansion in the range of from about 4.0 l0 to about 5.4 1O inch/inehl" C. It is to be understood that the silicon carbide coating could be applied to seal elements of other chemical composition, such as tungsten or molybdenum without departing from the scope of the present invention. A method of applying a silicon carbide coating to a base element is disclosed in U.S. Pat. No. 3.250.322 to J. W. McCrary, Jr. et al., patented May I0, 1966.

The seal elements of this invention will withstand the severe environmental conditions of the drilling operation. The surfaces of the seal elements may be machined to a smooth finish and is extremely hard and resistant to abrasion. Although the seal elements have been shown as being held in position by resilient mounting rings, it is to be understood that other means of retaining the seal elements in position may be provided. For example, the seal elements may be affixed to the elements of the bit by a suitable adhesive. It is also to be understood that the seal elements may be held in position by the particular geometry of the bit and the mounting rings may not be required in certain embodiments of the invention. lt can be appreciated that the seal thus provided has a long lifetime and effectively retains lubricant in the vicinity of the bearings.

The embodiments of the invention, in which an exclusive property or privilege is claimed are defined as follows:

1. An earth-boring bit comprising:

a main bit body;

a shaft connected to said main bit body;

a cutter rotatably mounted on said shaft;

bearing means between said shaft and said cutter for facilitating rotation of said cutter; and

seal means between said shaft and said cutter, said seal means having a silicon carbide surface.

2. The bit of claim 1 wherein said seal means is an annular ring with a silicon carbide surface.

3. The bit of claim 2 wherein said annular ring is graphite with a silicon carbide coating.

4. The bit of claim 1 where said seal means includes two annular rings, one ring positioned on each side of said bearing means, said annular rings having a silicon carbide surface.

5. The bit of claim 4 wherein said annular rings are graphite with a silicon carbide coating.

6. The bit of claim 1 wherein said seal means includes four annular rings, two rings positioned on each side of said bearing means, at least two of said annular rings have a silicon carbide surface.

7. The bit of claim 5 wherein at least two of said annular rings are graphite with a silicon carbide coating.

8. The bit of claim 5 wherein all four annular rings are graphite with a silicon carbide coating.

9. The bit of claim 1 wherein said seal means includes at least one annular ring with a silicon carbide surface and at least one resilient mounting ring positioned between said cutter and said annular ring.

10. A bit for boring through earth formations by the rotary method, comprising:

a main bit body;

a multiplicity of shafts connected to said main bit body;

a multiplicity of cutter means for disintegrating portions of the formations, said cutter means rotatably mounted on said shafts;

a multiplicity of bearing means, said bearing means positioned between said shafts and cutter means for facilitating rotation of said cutter means;

a multiplicity of lubricant reservoirs, said lubricant reservoirs positioned between said shafts and said cutter means, each said lubricant reservoir in communication with an individual bearing means; and

a multiplicity of seal means, with at least one seal means encircling each shaft between said shaft and said cutter means and positioned to retain lubricant in said lubricant reservoir, said seal means having a silicon carbide surface.

ll. The bit of claim 10 wherein said seal means includes an annular graphite ring with a silicon carbide coating, said ring positioned near one edge of an individual cutter means.

12. The bit of claim 10 wherein said seal means includes a multiplicity of annular graphite rings eaeh ring having a sillCOl'l carbide coating, one indlvidua ring positioned on each side of a lubricant reservoir.

13. The bit of claim 10 wherein said seal means includes two annular graphite rings with silicon carbide coatings, affixed to each of said shafts, and two annular graphite rings withsilicon carbide coatings, affixed to each individual cutter means. 

1. An earth-boring bit comprising: a main bit body; a shaft connected to said main bit body; a cutter rotatably mounted on said shaft; bearing means between said shaft and said cutter for facilitating rotation of said cutter; and seal means between said shaft and said cutter, said seal means having a silicon carbide surface.
 2. The bit of claim 1 wherein said seal means is an annular ring with a silicon carbide surface.
 3. The bit of claim 2 wherein said annular ring is graphite with a silicon carbide coating.
 4. The bit of claim 1 where said seal means includes two annular rings, one ring positioned on each side of said bearing means, said annular rings having a silicon carbide surface.
 5. The bit of claim 4 wherein said annular rings are graphite with a silicon carbide coating.
 6. The bit of claim 1 wherein said seal means includes four annular rings, two rings positioned on each side of said bearing means, at least two of said annular rings have a silicon carbide surface.
 7. The bit of claim 5 wherein at least two of said annular rings are graphite with a silicon carbide coating.
 8. The bit of claim 5 wherein all four annular rings are graphite with a silicon carbide coating.
 9. The bit of claim 1 wherein said seaL means includes at least one annular ring with a silicon carbide surface and at least one resilient mounting ring positioned between said cutter and said annular ring.
 10. A bit for boring through earth formations by the rotary method, comprising: a main bit body; a multiplicity of shafts connected to said main bit body; a multiplicity of cutter means for disintegrating portions of the formations, said cutter means rotatably mounted on said shafts; a multiplicity of bearing means, said bearing means positioned between said shafts and cutter means for facilitating rotation of said cutter means; a multiplicity of lubricant reservoirs, said lubricant reservoirs positioned between said shafts and said cutter means, each said lubricant reservoir in communication with an individual bearing means; and a multiplicity of seal means, with at least one seal means encircling each shaft between said shaft and said cutter means and positioned to retain lubricant in said lubricant reservoir, said seal means having a silicon carbide surface.
 11. The bit of claim 10 wherein said seal means includes an annular graphite ring with a silicon carbide coating, said ring positioned near one edge of an individual cutter means.
 12. The bit of claim 10 wherein said seal means includes a multiplicity of annular graphite rings, each ring having a silicon carbide coating, one individual ring positioned on each side of a lubricant reservoir.
 13. The bit of claim 10 wherein said seal means includes two annular graphite rings with silicon carbide coatings, affixed to each of said shafts, and two annular graphite rings with silicon carbide coatings, affixed to each individual cutter means. 